The study which I propose will examine the regulation of cyclic nucleotide metabolism in vascular endothelium, a tissue which has not been well-characterized biochemically. Collagenase digestion of hamster adipose tissue will provide relatively homogeneous suspensions of capillary endothelium for metabolic studies. Cultures of vascular endothelium will offer still another means of obtaining endothelial cells for biochemical experiments. Intracellular levels of cyclic AMP and cyclic GMP together with adenylate cyclase, guanylate cyclase, cyclic nucleotide phosphodiesterase, and cyclic nucleotide-dependent protein kinase constitute a vital cellular regulatory system which could be involved in endothelial permeability. Levels of the cyclic nucleotides and the activities of the enzymes will consequently be determined in endothelial preparations. The effects of hormones, drugs, and ions on these parameters in vascular endothelium will be assessed. In addition, endothelial glycogen metabolism and glucose utilization will be investigated. Aberrant endothelial function has been suggested as a factor in the development of some forms of circulatory disease, e.g., atherosclerosis. Endothelial changes are particularly prominent components of the diffuse vascular degeneration seen in patients with diabetes mellitus. Experimental diabetes mellitus can be produced in laboratory animals from which capillary endothelium can be isolated. Therefore, my research program will also consider the effects of acute and chronic insulin deficiencies on cyclic nucleotide metabolism and cyclic nucleotide-mediated processes in vascular endothelium. It is conceivable that abnormal metabolic patterns in endothelium play a role in the pathogenesis of diabetic angiopathies in man.